Integrated circuits, which are fabricated in recent years, are ultra-scale-large integrated circuits. The integration of integrated circuits continuously increases and the line-width of integrated circuited decreases at the same time. In the fabrication of ULSI circuits, a planarization process for a thin film on a wafer is a critical technique. The planarization process, which is adopted in a conventional process of integrated circuits, uses spin-on glass as a dielectric layer to refill voids on wafers. However, this conventional planarization process is a local planarization process for dielectric layer in integrated circuits and the process can not be applied on other materials used in integrated circuits.
A planarization process, which is called as chemical mechanical polishing technique, provides global planarization ability for dielectric material. This kind of planarization process has become a trend of a planarization process for ULSI circuits. A chemical mechanical polishing process is performed in chemical mechanical polishing (CMP) equipment to polish surfaces of semiconductor's wafers. During wafers are polished on a pad in the CMP equipment, slurry is scattered over the pad, the polished surface of the wafer contacts with the pad and the wafers are rotated for polishing the polished surface. According to the design requirement of integrated circuits, a thin film layer, which is polished, on a wafer after the planarization process must have a thickness being accepted by a specification to make sure that the film has an adequate thickness.
Because of the design of the conventional chemical mechanical polishing equipment, wafers have to be moved out the CMP equipment, then cleaned and dried before the thickness measurement of the polished thin film layer. The conventional thickness measurement is applied on wafers without any water or solution thereon. The limitation of the thickness measurement technique has influence on the flow chart of the chemical mechanical polishing process of wafers. Thus, a special flow chart is adopted for controlling the movements of wafers in the chemical mechanical polishing equipment. A flow chart of a chemical mechanical polishing process within conventional chemical mechanical polishing equipment is explained as below.
Referring to FIG. 1, a flow chart of a semiconductor wafer polished in a chemical mechanical polishing (CMP) equipment is demonstrated. First, in Step 200, a semiconductor wafer is loaded into a CMP equipment. Step 200 is followed by Step 210; the semiconductor wafer is put on a loading table for a preliminary position before a CMP process. In Step 220, CMP process is performed on the semiconductor wafer that is fixed to a polishing head. The wafer is put on a polishing head for globally polishing the main surface of the semiconductor wafer. After the semiconductor wafer is polished, Step 230 is performed to transfer the wafer to an unloading table before the wafer is removed from the CMP equipment. Step 240 is to transfer the semiconductor wafer a scrubbing apparatus for cleaning slurries on the wafer. In Step 250, the semiconductor wafer is transferred into an unload cassette and is unloaded from the CMP equipment. As Step 250 is completed, the CMP process of the wafer is finished. Following Step 250, Step 255 is performed to move the wafer out from the CMP equipment. In Step 260, the semiconductor wafer is cleaned and dried to remove contamination and solvent on the surface of the wafer. In Step 270, the thickness of the polished thin film layer is measured by using a thickness measurement apparatus. In Step 280, it is determined whether or not the thickness is accepted by a specification of the CMP process. As the thickness is not accepted by the specification, Step 282 is then performed. As the thickness is accepted by the specification, Step 281 is performed to remove the wafer out the CMP equipment. In Step 282, while the thickness of the polished thin film layer is less than the low limit of the specification, then Step 290 is performed for the deposition of the polished thin film layer. In Step 282, as the thickness of the polished thin film layer is not less than the low limit of the specification, Step 200 is performed again for keeping on the CMP process.
The flow chart, as mentioned in the above description, carries out in conventional CMP equipment. In the above flow chart, it is noted that the semiconductor wafer moves out the CMP equipment in a conventional CMP process before the cleaning and drying process of the wafer. The thickness measurement of the polished thin film layer executes after the slurry on the wafer is removed. The design of the flow chart is based on the limitation of the thickness measuring technique. The thickness measurement of the semiconductor wafer has to be executed outside the CMP equipment. As the thickness of the polished thin film layer is not accepted by the specification of the CMP process, the CMP process must keep on the semiconductor wafer. Alternatively, the polished thin film layer is deposited and the CMP process is then performed on the wafer. Furthermore, before the second CMP process of the semiconductor wafer is used, the wafer must be cleaned and dried, the flow chart becomes very complicated. If a new CMP process is performed on the semiconductor wafer, the flow chart must start from the beginning again. It takes too much time for the flow of the wafer and the cost of the CMP process is increased at the same time.
In a conventional CMP process, an end-point detector is applied for detecting the thickness of a polished thin film layer. The technique, using an end-point detector, measures the thickness of the polished thin film layer on a small area (normally, on peripheral area) of a wafer during a CMP process. Besides, the wafer is polished in a rotary way. The peripheral surface of the wafer has a different rotating rate from that of the central surface of the wafer. Similarly, there is a different polishing rate between the peripheral region and central region. The prior end-point detector just detects the some peripheral regions around the wafer and not the entire region over the wafer. According to this kind of measuring technique, measuring errors easily occurs and the thickness of the polished thin film layer can not be accurately determined.
Therefore, what is needed is a CMP process with an in-line thickness measurement. A thickness measurement is carried out in CMP equipment without removing wafers out the CMP equipment. The wafers do not be cleaned and dried until the CMP process of the wafers is finished. The polished thin film layer is detected in the CMP equipment to determine whether or not the CMP process is continued.